The object of the invention is a method for separating a component of interest bound to magnetic particles from a liquid sample by applying magnetic and centrifugal forces, wherein the centrifugal force is diametrically effective to the direction of the force which is effective to the magnetic particles by the magnetic field, and the magnetic force is higher than the centrifugal force effective to the magnetic particles, and thereby separating the magnetic particles from the liquid. The separated liquid is detained by a trap, the trapped liquid is preferably in addition bound to an adsorptive material. A further object of the invention is a device for carrying out the method.
Methods for isolating biological materials, especially nucleic acids from their natural environment with the help of magnetic particles are known since years (e.g., EP 0 837 871). According to the known methods, the sample mixture comprising the component of interest to be separated is brought into contact with the magnetic particles, mixed and incubated, under conditions where the compound of interest binds to the particle, for a period of time sufficient for the binding to occur. After incubation, the biological material bound to the magnetic particles is usually separated from the fluid by using a magnetic field. For instance, the magnetic particles can be pulled to the wall of the vessel or a pipette in which incubation was performed. The fluid containing the sample contents not bound to the magnetic particles are subsequently eliminated, e.g., via a pipette by aspiration.
These procedures have, however, a disadvantage in that a particular amount of the magnetic particles are sticking to the reaction vessel and/or the pipette tip.
Another disadvantage of removing the sample fluids by pipetting or aspiration is that either extensive assemblies, e.g., robotic machines, are required or the deficiency of manual handling has to be accepted. Moreover, extended time is required to draw magnetic particles out of the liquid or suspension by applying magnetic forces and to have those subsequently sufficiently washed (usually 3 to 4 times). Another disadvantage is that the magnetic particles collected mass or clumps tend to retain excessive fluid, the clumped mass is difficult to resuspend into solution.
U.S. Pat. No. 5,098,845 (Babson) describes a circular vessel containing a rather large sphere (solid support) to which specific analytes, e.g., antibodies, are attached. Washing separation is effected by rotating the cup about its longitudinal axis where centrifugal force serves to remove the liquid contents while the solid material remains in the vessel. The method has, however, the disadvantage similar to coated containers in that the surface area available for binding is limited to the dimension of the sphere. Yet another disadvantage is that the coated vessel cannot be used for micro spheres and especially not for magnetic micro spheres.
U.S. Pat. No. 6,150,182 (Cassaday) describes a method for combining magnetic and centrifugal extraction techniques in a manner that improves wash efficiency and reduces disadvantages of stand alone magnetic or centrifugal systems. A disadvantage of the method is, however, that it is difficult, if at all possible, to automate the procedure. Moreover, the method described by Cassaday does not overcome the disadvantages which are associated with the method of removing the sample fluids by pipetting or aspiration.
The devices and methods known have the disadvantage that they do not allow the separation of a component of interest bound to magnetic particles from a solution in an easy, sufficient manner without the need of any robotic means or without the risk involved with manual handling of samples.